NEW ORLEANS -- It's all in the way you look at things, maybe. You can measure what one person adds to the world. Or you can see what's missing when he's gone.

The Tulane football team practices on a humid Wednesday morning, and No. 18 is not in his spot at free safety.

In the defensive backs' meeting, no one sits in the top row, next to last seat. No one cracks jokes and doles out Sour Patch Kids and white chocolate.

In Nancy Hopkins' class, there's an empty space down front. The student who helps her gauge her lectures -- if he looks puzzled, the class is probably puzzled; if he gets it, they're getting it -- is absent

At the apartment five players share, the chef isn't there to cook sweet potato fries. The DJ who spins Lil Wayne and Rick Ross at campus parties left his laptop behind in the room.

The room. Wide receiver Jacob Davis, one of the players living there, has a hard time walking past. The nameplate from his roommate's junior-year locker is fastened to the door.

No. 18. Devon Walker.

He is hurt, and he is far away.

* * *

Devon (say it DEV-uhn) ran at the man with the ball. This was two Saturdays ago, a road game at Tulsa, and Tulane was already down 35-3. The Golden Hurricane decided to go for another score on fourth down from the Tulane 33. It was the last play of the first half.

Tulsa H-back Willie Carter caught a pass over the middle and turned upfield. Tulane linebacker Zach Davis grabbed his right leg and held on. Carter struggled to get free. Tulane defensive tackle Julius Warmsley came at Carter from the left. Devon came from the right. They dove at Carter as he fell. They crashed together, head-to-head, over him.

Warmsley weighs 271 pounds. Devon weighs 173. Tulane coach Curtis Johnson had his back turned to the play -- he had taken off his headset and was heading to the tunnel for halftime. He heard an odd noise from the crowd. He turned back around. Everyone was looking at Devon. Devon wasn't moving.

"I kind of walked over and he was just laying there," Johnson says. "I remember him saying 'I can't breathe.' They worked on him, worked on him. Then they brought the ambulance."

Devon's neck was broken. He had surgery that Sunday in Tulsa. He has spent time on a ventilator, and he has been going through physical therapy and respiratory therapy. He's scheduled to move to a rehab hospital soon. The precise injury isn't clear -- his parents, Booker and Inez Walker, have requested privacy on some of the details. Those details matter. In a spinal injury, the location and type of the break makes all the difference in how the patient might recover. No one has disclosed those kinds of details about Devon Walker.

No one has said if he has a chance to walk again.

Johnson knew Devon long before Tulane. They're New Orleans born and raised. His brother-in-law is best friends with Devon's father. Johnson said he'd be more worried about some of his other players if they were in Devon's place.

"A lot of these kids, they don't prepare for their lives, they just live day to day," Johnson said. "What I like about this kid, he's a self-made man. He has some kind of major that I can't pronounce … He understood his future before it even happened."

* * *

The major is cell and molecular biology. Devon plans to be a pharmacist. He was an honors student at Destrehan High, where he started at safety for a team that went 29-0 his last two years. A couple of smaller schools offered him football scholarships. He chose to walk on at Tulane. He wanted to stay in New Orleans, and he wanted a college with strong academics.

Nancy Hopkins teaches upper-level classes for cell and molecular biology majors. It's one of the hardest majors at Tulane, and especially hard for athletes -- there's lots of lab work, and it's hard to wedge classes and labs around practices and games. Last spring, Devon and Jacob came to Hopkins' office with a request. Normally, organic chemistry is a prerequisite for her biochemistry class. Devon and Jacob wanted her permission to take both at the same time.

Just to be clear: Here are football players, not trying to get out of difficult classes, but doubling up on them.

"Devon charmed his way in," Hopkins said. "He is ex-treme-ly polite. Apologizes if he interrupts. Says thank you. Things that we should see in all our students, but we don't always."

Devon, Jacob and teammate Chris Hanuscin are all cell and molecular biology majors. They sit together in classes, always in the front row, Devon always in the middle. This fall Hopkins is teaching them in a class called Principles of Biomedical Writing. The first class after Devon got hurt was held in the library instead of the regular classroom. Hopkins was glad. She didn't know how she would react to looking down and seeing that empty seat.

Several professors in the department have checked in with Jacob and Chris. Others have reached out to Devon's family, which is with him in Tulsa. Everyone wants to go see Devon.

But he has to get better first. And they have their own lives to sort out.

"This is what everybody forgets about college football players," Hopkins said. "They deal with all these intense things. But they're kids. They're 20 years old. How do you handle this when you're 20 years old?"

* * *

They practice in the mornings before the damp New Orleans heat can smother them. Here in the lower reaches of FBS football, players still have the tools - just not all of them. A receiver breaks wide open but drops a perfect pass. A linebacker sheds a block but whiffs on the tackle. The punting team gets one blocked, and a coach slams his hat to the ground. But this is Tulane, and if nothing else, the players have quick minds. "You ain't no model," one coach yells at a player who took his helmet off between drills. A teammate, under his breath: "His girlfriend ain't either."

The Green Wave is 0-2 this year, 9-30 since Devon arrived in 2009. Through all those losses, he made a slow climb through the depth chart. As a walk-on his first two years, he played a lot of special teams. He went to summer school before his junior year and showed up for 6 a.m. team workouts even though he had to pay his own way. At the end of the summer, Bob Toledo -- then the Tulane coach -- gave Devon the team's last scholarship. The first thing Devon did was call his mom.

When he was a freshman, he ran around the field so wild and loose -- like a deer -- that secondary coach Jason Rollins nicknamed him Buck. But as a senior, Buck had calmed down. This year he won the starting job at free safety. He mentored the younger players. In position meetings he took that seat in the back row, scarfing snacks and calling out assignments before the coaches could.

After the injury, coach Johnson stayed on the field and sent everyone else back to the locker room. They gathered by position as they always do. Rollins and his defensive backs circled quietly in a corner. They said a prayer for Devon.  

"We've had some tough spots in practice since then," Rollins said. "It's strange to look for him on the field, or in a meeting, and have him not be there. I mean, you have to understand. He was a light bulb in our locker room."

* * *

Devon rooms with Jacob Davis (the receiver) and three cornerbacks: Ryan Travis, Kendrick Washington and Kendrell Washington. Kendrick and Kendrell are twins. They're all seniors. They've known one another their whole college lives.

To them, Devon has another nickname: Dookie. It's a name Devon picked up in high school. Nobody's quite sure why; Devon once said that it "came in the wind." When he gets the music going at parties, it morphs into DJ Dookie.

Dookie has red and blue lights in his room. He has speakers that make the floor shake. He has "Pulp Fiction" posters on the wall and a giant stash of movies on DVD (he loves the "Transformers" series) and a stream of movie quotes coming out of his mouth. He is polite to his professors. He talks ceaseless trash playing Call of Duty.

He is vain about his hair -- he hasn't cut it for years, and wears it in long dreadlocks. One of the first things Tulane athletic director Rick Dickson told Devon after he woke up from surgery was that the doctors didn't have to cut his hair.

Devon Walker is 21 years old, fully adult everywhere in America but the rental-car counter, grown enough to take on a tough major at a tough school, enough of a kid to obsess over video games and live on candy. It's an age where a young man with energy and ambition might never be more fully present.

But for now he is so far away, and all his friends sense is his absence.

Depending on his injury, and the details we do not know, there's a wide range of recovery. Eric LeGrand, the Rutgers linebacker hurt in 2010, is paralyzed from the shoulders down. Adam Taliaferro, the Penn State cornerback hurt in 2000, walked again within a year.

Devon can talk -- the doctors have said that much -- and at some point he'll get to see his coaches and teammates and friends again, and he'll start refilling the spaces he left behind.

But for now there are just the spaces.

Ryan looked across the aisle on the flight back from Tulsa, and Devon was not in his seat.

Jacob went in Devon's room to get his backpack, and the music wasn't playing.

They don't know when he'll be back. They don't know what that'll be like. So many at Tulane are living this odd life now, their student or friend or teammate or roommate up in Tulsa, still not back from the game.

Kendrick Washington, one of the roommates, doesn't play much. He wasn't on the traveling team for Tulsa. A couple days after the game, when his alarm went off at 5:30 a.m. for practice, the groggy part of his brain decided it wasn't worth it, so much sacrifice for so little. He cut the alarm and rolled back over.

Then his head cleared, and he had one thought.

Devon would get up.

And so he got up, and went to practice, and Tulane will play Ole Miss on Saturday, and Principles of Biomedical Writing will keep meeting, and everything will go back to normal, except not quite, because they are still minus one.

* * *

Tulane has started a fund to raise money for Devon Walker's recovery. Go here to make direct donations, or go here to buy a T-shirt whose proceeds go to the fund.

The University of Tulsa has started its own fund to help cover the Walker family's costs while staying with Devon in Tulsa.

You can also donate to the College Football Assistance Fund, which helps injured college football players and has given $10,000 to Tulane for Devon's care.